For the purpose of reducing power consumption or heat generation, PWM control is adopted to supply an electromagnetic inductive load, such as relay coil and electromagnetic clutch, with power from a power source. Then, during a power-off period of PWM control where the power supply from the power source to the electromagnetic inductive load is turned off, regeneration current flows. By switching power-off to power-on of PWM control to restart the power supply to the electromagnetic inductive load before the regeneration current flows below a minimum value of current required to drive the electromagnetic inductive load, it is possible to reduce power consumption or heat generation while maintaining the driving of the electromagnetic inductive load.
In the case of performing PWM control mentioned above, it is indispensable to detect a regeneration current value flowing through the electromagnetic inductive load in order to determine an appropriate timing of switching the power supply from the power source to the electromagnetic inductive load from its on-state to off-state. In the past, therefore, inventors of the present application et al. proposed an electromagnetic inductive load control device configured to allow the regeneration current to flow through a shunt resistor via a diode to detect a regeneration current value from a potential difference between both ends of the shunt resistor and control power-on in PWM control based on the detected regeneration current value (refer to JP 2011-188226 A).
In the control device according to this proposal, the potential on an anode side of the diode becomes higher than the potential of the power source. Therefore, drop circuits for voltage drop are provided at both ends of the shunt resistor respectively to protect a detection part for detecting the potential difference between both ends of the shunt resistor from a high voltage potential.